Calibration of the OdysseyTM Photosynthetic Irradiance RecorderTM for absolute irradiance measures

Abstract

The OdysseyTM Photosynthetic Irradiance RecorderTM is an affordable photosynthetically-active radiation (PAR) meter gaining popularity among aquatic ecologists. A survey of the literature revealed that the instrument is frequently being used for absolute measures of PAR, although its design was intended for relative measures only. Unlike more expensive PAR meters, the OdysseyTM Recorder must be user calibrated. We found the suggested two-point calibration procedure could produce inaccuracies ranging from less than 1% to greater than 300%. The calibration procedure is therefore not suitable for absolute measures or for comparison studies. We recommend a revised calibration procedure that is unaffected by shortterm fluctuations in solar intensity. Furthermore, this procedure yields a calibration factor and standard error. Accuracy is critical for investigations which seek to compare PAR measurements made with multiple sensors or to build quantitative relationships between processes and PAR. © 2012 Taylor & Francis.